Mid-phase microemulsions, their preparation methods and applications

Abstract

This invention provides a medium-phase microemulsion, its preparation method, and its application. The medium-phase microemulsion comprises a surfactant, surfactant auxiliaries, inorganic salts, crude oil, and water. The surfactant is an anionic nonionic surfactant, including the surfactant APEG-LY-SSS, with the following structural formula: [Formula omitted for brevity]. Wherein, 5≤x≤15, 2≤y≤20, 4≤z≤10, R1 is H or CH3, and R2 is a C2-C18 alkyl, hydroxyethyl, hydroxypropyl, or methoxy group. The medium-phase microemulsion prepared by this invention exhibits excellent anti-adsorption properties, strong temperature resistance, and strong salt resistance, showing broad prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemistry, and more specifically, to a medium-phase microemulsion, its preparation method, and its application. Background Technology

[0002] Microemulsions are isotropic colloidal dispersions that spontaneously form from water, surfactants, cosolvents, and oil. Due to their large specific surface area, small particle size, low interfacial tension, and unique solubilization and penetration capabilities, they are widely used in the petroleum industry, especially in the field of enhanced oil recovery.

[0003] Based on the water-oil equilibrium state in microemulsions, Winsor classifies microemulsions into four types. Winsor Type I microemulsions are multiphase systems where an O / W microemulsion and an excess oil phase coexist. Winsor Type II microemulsions are multiphase systems where a W / O microemulsion and an excess aqueous phase coexist. Between these two multiphase systems lies another morphological state, called Winsor Type III microemulsions, which refer to bicontinuous microemulsions of oil and water. In this type, both the oil and water phases are continuous and dispersed, forming a network structure without obvious oil or water droplets; this is also called a mid-phase microemulsion. Winsor Type IV microemulsions refer to single-phase microemulsions, which can also be divided into O / W, W / O, and bicontinuous types.

[0004] For the Winsor III type microemulsion system, this medium-phase microemulsion can form a miscible oil wall with the reservoir residual oil, which plays a crucial role in microemulsion oil displacement, thereby achieving highly efficient displacement and significantly higher oil washing efficiency compared to the other two types of microemulsions. Chinese invention patent (application number 202110388654.6) discloses an in-situ generated medium-phase microemulsion oil washing system, specifically disclosing that the system composition includes anionic surfactants, nonionic surfactants, co-surfactants, and salts, and testing the oil washing efficiency at 25°C. However, the temperature resistance and anti-adsorption properties of this system still need improvement.

[0005] Therefore, existing medium-phase microemulsions suffer from problems such as poor temperature resistance or poor adsorption resistance, and there is an urgent need to provide a medium-phase microemulsion and its preparation method to improve these problems. Summary of the Invention

[0006] The main objective of this invention is to provide a medium-phase microemulsion, its preparation method, and its application, in order to solve the problems of poor temperature resistance or poor anti-adsorption in existing medium-phase microemulsions.

[0007] To achieve the above objectives, according to one aspect of the present invention, a mid-phase microemulsion is provided, comprising a surfactant, a surfactant auxiliary, an inorganic salt, crude oil, and water; wherein the surfactant is an anionic nonionic surfactant, and the surfactant includes the surfactant APEG-LY-SSS, whose structural formula is: Wherein, 5≤x≤15, 2≤y≤20, 4≤z≤10, R1 is H or CH3, and R2 is a C2~C18 alkyl, hydroxyethyl, hydroxypropyl or methoxy group.

[0008] Furthermore, in addition to the surfactant APEG-LY-SSS, the surfactant also includes one or more of sodium fatty alcohol polyoxyethylene ether sulfonate, sodium dodecyl sulfate, sodium alkyl diphenyl ether disulfonate or petroleum sulfonate, more preferably sodium fatty alcohol polyoxyethylene ether sulfonate; preferably, the weight ratio of surfactant APEG-LY-SSS to sodium fatty alcohol polyoxyethylene ether sulfonate is 1:(1 to 10) by weight percentage.

[0009] Furthermore, by weight percentage, the components of the medium-phase microemulsion include 0.5–4.5 wt% surfactant, 1.5–6.5 wt% surfactant auxiliaries, 0.5–4.0 wt% inorganic salt, 85.0–97.5 wt% crude oil, and the balance being water.

[0010] Furthermore, the surfactant is selected from alcohol solvents, preferably one or more of n-hexanol, n-butanol or n-pentanol; the inorganic salt is preferably sodium chloride and / or potassium chloride.

[0011] Furthermore, the components of the medium-phase microemulsion include 1.2–4.5 wt% surfactant, 2.5–5.5 wt% surfactant auxiliaries, 0.5–2.5 wt% inorganic salt, 87.5–94.5 wt% crude oil, and the balance water; preferably, the water is reinjected wastewater and / or tap water.

[0012] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a medium-phase microemulsion is provided, the method comprising: step S1, taking a surfactant, an inorganic salt and water and stirring them once in a stoppered colorimetric tube to obtain a mixed solution; step S2, taking a surfactant and crude oil and stirring them a second time in the mixed solution to obtain a medium-phase microemulsion.

[0013] Further, by weight percentage, the weight ratio of surfactant additive, inorganic salt and water is 1:(0.2-2.5):(30-70); preferably, the weight ratio of surfactant to crude oil is (0.01-0.30):1.

[0014] Furthermore, the stirring speed is 100-500 rpm, the stirring time is 0.1-1.0 h, and the stirring temperature is 20-50℃.

[0015] Furthermore, the secondary stirring speed is 200-400 rpm, the secondary stirring time is 0.5-2.0 h, and the secondary stirring temperature is 20-50℃.

[0016] According to another aspect of the present invention, a medium-phase microemulsion or a medium-phase microemulsion prepared by the above-mentioned method is provided for application in the fields of oil and gas field development, deep water shut-off and profile control, or tertiary oil recovery.

[0017] The medium-phase microemulsion prepared by applying the technical solution of this invention has excellent anti-adsorption properties, strong temperature resistance and salt resistance, and has broad prospects for industrial application. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 The volume distribution diagram of the nanoparticle size of the mid-phase microemulsion in Example 1 of this invention is shown. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] According to the background section of this invention, existing medium-phase microemulsions suffer from problems such as poor temperature resistance or poor anti-adsorption. To address these problems, this invention provides a medium-phase microemulsion comprising a surfactant, surfactant auxiliaries, an inorganic salt, crude oil, and water; wherein the surfactant is an anionic nonionic surfactant, including surfactant APEG-LY-SSS, with the following structural formula: Wherein, 5≤x≤15, 2≤y≤20, 4≤z≤10, R1 is H or CH3, and R2 is a C2~C18 alkyl, hydroxyethyl, hydroxypropyl or methoxy group.

[0022] The medium-phase microemulsion system provided by this invention contains a surfactant component, which is an anionic nonionic surfactant, particularly APEG-LY-SSS. Firstly, the surfactant has a large number of ethoxy groups on its side chains, giving the medium-phase microemulsion system excellent water solubility and interfacial activity. Secondly, the surfactant in this invention has numerous benzene ring groups on its structural segments, which enhances the rigidity of its molecular chain and improves its temperature resistance and shear resistance. Furthermore, the three oxygen atoms in the -SO3- structure of the sulfonic acid group share two π bonds and a negative charge, further enhancing its stability and making it unaffected by cations present in the environment (such as Ca2+). 2+ Mg 2+ Due to the influence of factors such as temperature and salt resistance, the sulfonate ions loaded on its chain segments give the surfactant excellent temperature and salt resistance. Finally, the hydrophobic long chains on its chain segments adjust the HLB value of the surfactant, making it suitable for various oil phases, significantly improving its compatibility in microemulsion formulation, reducing interfacial tension, and enhancing its anti-adsorption properties. In summary, the surfactant APEG-LY-SSS in this invention, with its long-chain structure, improves the temperature resistance and anti-adsorption properties of the mid-phase microemulsion system to a certain extent. The large amount of oxyethylene ether structures in its structure also reduces interfacial tension, thus giving the mid-phase microemulsion system of this invention good temperature resistance and anti-adsorption properties. Experiments have shown that the mid-phase microemulsion system of this invention achieves a viscosity of 15 mPa·s at 95℃ and a salinity of 26000 mg / L, and can form a 10... -3 With an ultra-low interfacial tension of mN / m, the adsorption amount in oil sand after 24 hours is around 9mg / g, demonstrating good temperature resistance and anti-adsorption properties.

[0023] In a preferred embodiment, in addition to the surfactant APEG-LY-SSS, the surfactant also includes one or more of sodium fatty alcohol polyoxyethylene ether sulfonate, sodium dodecyl sulfate, sodium alkyl diphenyl ether disulfonate, or petroleum sulfonate, more preferably sodium fatty alcohol polyoxyethylene ether sulfonate. More preferably, the weight ratio of surfactant APEG-LY-SSS to sodium fatty alcohol polyoxyethylene ether sulfonate is 1:(1-10) to further improve its compatibility in the preparation of medium-phase microemulsions, reduce interfacial tension, and improve its anti-adsorption performance.

[0024] In a preferred embodiment, the components of the medium-phase microemulsion, by weight percentage, include 0.5–4.5 wt% surfactant, 1.5–6.5 wt% surfactant auxiliaries, 0.5–4 wt% inorganic salt, 85.0–97.5 wt% crude oil, and the balance water, thereby further improving the anti-adsorption and temperature resistance of the medium-phase microemulsion system.

[0025] To further improve the solubilizing and wetting properties of the medium-phase microemulsion system and enhance its dispersibility, the preferred surfactant is an alcohol solvent, further selected from one or more of n-hexanol, n-butanol, or n-pentanol, and the preferred inorganic salt is sodium chloride and / or potassium chloride.

[0026] To further improve the anti-adsorption and temperature resistance of the medium-phase microemulsion system, the preferred components of the medium-phase microemulsion include 1.2–4.5 wt% surfactant, 2.5–5.5 wt% surfactant auxiliaries, 0.5–2.5 wt% inorganic salt, 87.5–94.5 wt% crude oil, and the balance water; more preferably, the water is reinjected wastewater and / or tap water.

[0027] In another aspect, the present invention provides an improved method for preparing a mid-phase microemulsion. This method includes: step S1, stirring a surfactant, inorganic salt, and water in a stoppered colorimetric tube to obtain a mixed solution; and step S2, stirring a surfactant and crude oil in the mixed solution a second time to obtain the mid-phase microemulsion. The mid-phase microemulsion prepared by this method exhibits excellent temperature resistance and anti-adsorption properties. Furthermore, the preparation method is simple and easy to operate, suitable for large-scale production, and has broad prospects for industrial application.

[0028] In a preferred embodiment, the weight ratio of surfactant, inorganic salt and water is 1:(0.2-2.5):(30-70); thereby preparing the prepared medium-phase microemulsion and further improving its temperature resistance and anti-adsorption properties. More preferably, the weight ratio of surfactant to crude oil is (0.01-0.3):1.

[0029] To further improve the uniform dispersion of components in the medium-phase microemulsion system, the stirring speed for the first stirring is 100–500 rpm, the stirring time for the first stirring is 0.1–1.0 h, and the stirring temperature for the first stirring is 20–50 °C; the stirring speed for the second stirring is further preferred to be 200–400 rpm, the stirring time for the second stirring is 0.5–2.0 h, and the stirring temperature for the second stirring is 20–50 °C.

[0030] Another aspect of the present invention provides a method for preparing the surfactant APEG-LY-SSS: Allyl polyoxyethylene ether, sodium styrene sulfonate, and deionized water are mixed and added to a three-necked flask equipped with a stirrer. The mixture is stirred in a constant temperature water bath at 40–60°C. Then, under water bath conditions at 65–80°C, a mixture of acrylate monomers and isopropanol, along with an aqueous solution of ammonium persulfate, is added. The reaction is carried out for 1–5 hours, cooled to room temperature, and the product is washed with acetone, dried, and ground into powder. The acrylate monomers are preferably one or more of lauryl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, methyl methacrylate, or octadecyl acrylate.

[0031] To further improve the reactivity of the surfactant APEG-LY-SSS and increase its reaction conversion rate and product yield, the preferred weight ratio of allyl polyoxyethylene ether, sodium styrene sulfonate, and deionized water is (0.05-0.25):(0.05-0.15):1; and the preferred acrylate monomer accounts for 35-50 wt% of the mixture of acrylate monomer and isopropanol.

[0032] Another aspect of the present invention provides the application of a medium-phase microemulsion obtained by a method for preparing a medium-phase microemulsion in the fields of oil and gas field development, deep water shut-off and profile control, or tertiary oil recovery.

[0033] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0034] Example 1

[0035] Mix 2g of allyl polyoxyethylene ether, 1g of sodium styrene sulfonate, and 10mL of deionized water, and add the mixture to a three-necked flask equipped with a stirrer. Stir the mixture thoroughly in a 60℃ constant temperature water bath. Simultaneously add a mixture of lauryl acrylate and isopropanol, and an aqueous solution of ammonium persulfate (2g of lauryl acrylate dissolved in 2mL of isopropanol, and 0.32g of ammonium persulfate dissolved in 0.68g of deionized water to form an initiator aqueous solution) dropwise under 75℃ water bath conditions. React for 3 hours, cool to room temperature, wash the product with acetone, dry it, and grind it into powder to prepare the surfactant APEG-LY-SSS, denoted as APEG-LY-SSS-A, with the structural formula: Where x = 10, y = 15, z = 8.

[0036] 0.7 g of sodium chloride, 1.5 g of n-butanol, and 2 g of water were added to a stoppered colorimetric tube and stirred once at 400 rpm for 0.5 h at 30 °C to prepare a mixed solution of salt and n-butanol. 0.25 g of sodium fatty alcohol polyoxyethylene ether sulfonate, 0.15 g of APEG-LY-SSS-A, and 0.3 g of sodium dodecyl sulfate were added to the above mixed solution. Then, 14 mL of reinjected wastewater and 16 mL of crude oil were added and stirred a second time at 300 rpm for 1 h at 30 °C to obtain a medium-phase microemulsion. Figure 1 The volume distribution diagram of the nanoparticle size of the medium-phase microemulsion is shown.

[0037] The components of the medium-phase microemulsion include: 2.03 wt% surfactant, 3.19 wt% surfactant additive, 2.03 wt% inorganic salt, 92.75 wt% crude oil, and the balance water; wherein the surfactant includes (relative to the total mass) 0.73 wt% sodium fatty alcohol polyoxyethylene ether sulfonate, 0.43 wt% APEG-LY-SSS-A, and 0.87 wt% sodium dodecyl sulfate.

[0038] Example 2

[0039] The only difference from Example 1 is that the raw materials for the medium-phase microemulsion are 0.3g of sodium chloride, 1.8g of n-butanol, 0.15g of sodium fatty alcohol polyoxyethylene ether sulfonate and 0.25g of petroleum sulfonate.

[0040] The components of the medium-phase microemulsion include: 1.59 wt% surfactant, 5.19 wt% surfactant additive, 0.87 wt% inorganic salt, 92.35 wt% crude oil, and the balance water; wherein the surfactant includes (relative to the total mass) 0.44 wt% sodium fatty alcohol polyoxyethylene ether sulfonate, 0.43 wt% APEG-LY-SSS-A, and 0.72 wt% petroleum sulfonate.

[0041] Example 3

[0042] 2g of allyl polyoxyethylene ether, 1g of sodium styrene sulfonate, and 10mL of deionized water were mixed and added to a three-necked flask equipped with a stirrer. The mixture was stirred evenly in a constant temperature water bath at 50℃. Simultaneously, a mixture of hydroxyethyl methacrylate and isopropanol, and an aqueous solution of ammonium persulfate (2g of hydroxyethyl methacrylate dissolved in 2mL of isopropanol, and 0.32g of ammonium persulfate dissolved in 0.68g of deionized water to form an initiator aqueous solution) were added dropwise under a water bath at 80℃. The reaction was allowed to proceed for 4 hours, then cooled to room temperature. The product was washed with acetone, dried, and ground into powder to prepare the surfactant APEG-LY-SSS, denoted as APEG-LY-SSS-B. Its structural formula is... Where x = 8, y = 20, z = 4.

[0043] The preparation steps of the medium-phase microemulsion differ from those in Example 1 in that the raw materials used are 0.4g of potassium chloride, 0.16g of sodium fatty alcohol polyoxyethylene ether sulfonate, 0.1g of APEG-LY-SSS-B, and an additional 0.15g of petroleum sulfonate.

[0044] The components of the medium-phase microemulsion include: 2.05 wt% surfactant, 4.33 wt% surfactant additive, 1.16 wt% inorganic salt, 92.46 wt% crude oil, and the balance water; wherein the surfactant includes (relative to the total mass) 0.46 wt% sodium fatty alcohol polyoxyethylene ether sulfonate, 0.29 wt% APEG-LY-SSS-B, 0.43 wt% petroleum sulfonate, and 0.87 wt% sodium dodecyl sulfate.

[0045] Example 4

[0046] 2g of allyl polyoxyethylene ether, 1g of sodium styrene sulfonate, and 10mL of deionized water were mixed and added to a three-necked flask equipped with a stirrer. The mixture was stirred evenly in a constant temperature water bath at 40℃. Simultaneously, a mixture of octadecyl acrylate and isopropanol, and an aqueous solution of ammonium persulfate (2g of octadecyl acrylate dissolved in 2mL of isopropanol and 0.32g of ammonium persulfate dissolved in 0.68g of deionized water to form an initiator aqueous solution) were added dropwise under a water bath at 65℃. The reaction was allowed to proceed for 5 hours, then cooled to room temperature. The product was washed with acetone, dried, and ground into powder. The surfactant APEG-LY-SSS, denoted as APEG-LY-SSS-C, was thus prepared. Its structural formula is... Where x = 15, y = 2, z = 8.

[0047] The preparation steps of the medium-phase microemulsion differ from those in Example 1 in that the raw materials used are 0.6g sodium chloride, 1.8g n-butanol, 0.17g sodium fatty alcohol polyoxyethylene ether sulfonate, 0.1g APEG-LY-SSS-C, and an additional 0.15g sodium alkyl diphenyl ether disulfonate.

[0048] The components of the medium-phase microemulsion include: 2.05 wt% surfactant, 5.13 wt% surfactant additive, 1.71 wt% inorganic salt, 91.12 wt% crude oil, and the balance water; wherein the surfactant includes (relative to the total mass) 0.48 wt% sodium fatty alcohol polyoxyethylene ether sulfonate, 0.28 wt% APEG-LY-SSS-C, 0.43 wt% sodium alkyl diphenyl ether disulfonate, and 0.85 wt% sodium dodecyl sulfate.

[0049] Example 5

[0050] The only difference from Example 1 is that the raw materials for the medium phase microemulsion are 0.5g of sodium chloride, 1.8g of n-butanol, 0.25g of sodium fatty alcohol polyoxyethylene ether sulfonate, and 0.05g of APEG-LY-SSS-A.

[0051] The components of the medium-phase microemulsion include: 1.72 wt% surfactant, 5.16 wt% surfactant additive, 1.43 wt% inorganic salt, 91.69 wt% crude oil, and the balance water; wherein the surfactant includes (relative to the total mass) 0.72 wt% sodium fatty alcohol polyoxyethylene ether sulfonate, 0.14 wt% APEG-LY-SSS-A, and 0.86 wt% sodium dodecyl sulfate.

[0052] Example 6

[0053] 2g of allyl polyoxyethylene ether, 1g of sodium styrene sulfonate, and 10mL of deionized water were mixed and added to a three-necked flask equipped with a stirrer. The mixture was stirred evenly in a constant temperature water bath at 40℃. Simultaneously, a mixture of ethyl acrylate and isopropanol, and an aqueous solution of ammonium persulfate (2g of ethyl acrylate dissolved in 2mL of isopropanol and 0.32g of ammonium persulfate dissolved in 0.68g of deionized water to form an initiator aqueous solution) were added dropwise under a water bath at 65℃. The reaction was allowed to proceed for 5 hours, then cooled to room temperature. The product was washed with acetone, dried, and ground into powder. The surfactant APEG-LY-SSS, denoted as APEG-LY-SSS-D, was thus prepared. Its structural formula is... Where x = 5, y = 10, z = 10.

[0054] Example 7

[0055] The only difference from Example 1 is that the surfactant used is APEG-LY-SSS-C, whose structural formula is R2 is a substituent of a C18 alkane.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that the surfactant APEG-LY-SSS-A is not added.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that the weight ratio of surfactant APEG-LY-SSS-A to sodium fatty alcohol polyoxyethylene ether sulfonate is 1:0.1.

[0060] Comparative Example 3

[0061] The difference from Example 1 is that the weight ratio of surfactant APEG-LY-SSS-A to sodium fatty alcohol polyoxyethylene ether sulfonate is 1:15.

[0062] Comparative Example 4

[0063] The difference from Example 1 is that it contains 0.1 wt% surfactant.

[0064] Comparative Example 5

[0065] The difference from Example 1 is that it contains 10 wt% surfactant.

[0066] Performance testing:

[0067] 1) Temperature resistance

[0068] The medium-phase microemulsion was prepared into 0.01% aqueous solutions with water. The interfacial tension between the temperature-resistant and adsorption-resistant medium-phase microemulsion and crude oil was measured using a rotating drop interfacial tension meter at a speed of 3000-6000 rpm and at 95°C.

[0069] 2) Salt tolerance

[0070] The medium-phase microemulsion was prepared into 0.01% aqueous solutions with water and 26000 mg / L saline solution. The interfacial tension (in mN / m) between the temperature-resistant and adsorption-resistant medium-phase microemulsion and crude oil was measured using a rotating drop interfacial tensiometer at a speed of 3000–6000 rpm and a temperature of 25°C.

[0071] 3) Anti-adsorption properties

[0072] Take 10.00g of treated oil sand and add it to a 150mL conical flask with a stopper and ground glass. Then add 90g of a 0.01% aqueous solution of a temperature-resistant and anti-adsorption medium-phase microemulsion. Place the conical flask in a water bath constant temperature shaking chamber and shake for 24 hours at a shaking frequency of 90 times / min. Filter the clear liquid, test the absorbance of the clear liquid, and calculate the adsorption amount (unit: mg / g).

[0073] The medium-phase microemulsions prepared in the above examples and comparative examples were subjected to the above performance tests, and the results are shown in Table 1 below.

[0074] Table 1

[0075]

[0076] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0077] The test results of Examples 1 to 5 and Comparative Example 1 show that when the anionic nonionic surfactant of the present invention is used, including surfactant APEG-LY-SSS, the prepared medium-phase microemulsion has excellent anti-adsorption properties, strong temperature resistance and salt resistance.

[0078] The test results of Examples 1 to 5 and Comparative Examples 2 and 3 show that when the technical solution of the present invention is adopted, and the weight ratio of surfactant APEG-LY-SSS to sodium fatty alcohol polyoxyethylene ether sulfonate is 1:(1 to 10) by weight percentage, the prepared medium-phase microemulsion has excellent anti-adsorption properties and strong temperature resistance and salt resistance.

[0079] The test results of Examples 1 to 5 and Comparative Examples 4 and 5 show that when the components of the medium-phase microemulsion in the present invention contain 0.5 to 4.5 wt% surfactant, the medium-phase microemulsion has strong temperature resistance, salt resistance and anti-adsorption properties. However, when the content of surfactant components in the medium-phase microemulsion is higher than the upper limit or lower than the lower limit in the present invention, the anti-adsorption and temperature resistance of the medium-phase microemulsion are poor.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A medium-phase microemulsion, characterized in that, The medium-phase microemulsion comprises a surfactant, surfactant additives, inorganic salts, crude oil, and water; wherein the surfactant is an anionic nonionic surfactant, and the surfactant includes APEG-LY-SSS, whose structural formula is: Wherein, 5≤x≤15, 2≤y≤20, 4≤z≤10, R1 is H or CH3, and R2 is a C2~C18 alkyl, hydroxyethyl, hydroxypropyl or methoxy group; The surfactant also includes sodium fatty alcohol polyoxyethylene ether sulfonate, and the weight ratio of the surfactant APEG-LY-SSS to the sodium fatty alcohol polyoxyethylene ether sulfonate is 1:(1~10) by weight percentage. The components of the medium-phase microemulsion include 0.5 to 4.5 wt% of the surfactant by weight percentage.

2. The mid-phase microemulsion according to claim 1, characterized in that, The components of the medium-phase microemulsion, by weight percentage, also include 1.5 to 6.5 wt% of the surfactant additive, 0.5 to 4.0 wt% of the inorganic salt, 85.0 to 97.5 wt% of the crude oil, and the balance being water.

3. The mid-phase microemulsion according to claim 1, characterized in that, The surfactant additive is selected from alcohol solvents.

4. The mid-phase microemulsion according to claim 3, characterized in that, The surfactant additive is selected from one or more of n-hexanol, n-butanol, or n-pentanol.

5. The mid-phase microemulsion according to claim 1, characterized in that, The inorganic salt is sodium chloride and / or potassium chloride.

6. The medium-phase microemulsion according to any one of claims 1 to 5, characterized in that, The components of the medium-phase microemulsion include 1.2 to 4.5 wt% of the surfactant, 2.5 to 5.5 wt% of the surfactant auxiliaries, 0.5 to 2.5 wt% of the inorganic salt, 87.5 to 94.5 wt% of the crude oil, and the balance being water.

7. The mid-phase microemulsion according to claim 6, characterized in that, The water is recycled sewage and / or tap water.

8. A method for preparing a mid-phase microemulsion according to any one of claims 1 to 7, characterized in that, The preparation method includes: Step S1: Take surfactant additive, inorganic salt and water into a stoppered colorimetric tube and stir once to obtain a mixed solution; Step S2: Take the surfactant and crude oil into the mixed solution and stir it a second time to obtain the medium phase microemulsion.

9. The method for preparing the mid-phase microemulsion according to claim 8, characterized in that, The weight ratio of the surfactant additive, the inorganic salt, and water is 1:(0.2~2.5):(30~70) by weight percentage.

10. The method for preparing the mid-phase microemulsion according to claim 9, characterized in that, The surfactant is present in a weight ratio of (0.01~0.30):1 to the crude oil.

11. The method for preparing the medium-phase microemulsion according to any one of claims 8 to 10, characterized in that, The stirring speed for one stirring cycle is 100~500 rpm, the stirring time for one stirring cycle is 0.1~1.0 h, and the stirring temperature for one stirring cycle is 20~50℃.

12. The method for preparing the medium-phase microemulsion according to any one of claims 8 to 10, characterized in that, The secondary stirring speed is 200~400 rpm, the secondary stirring time is 0.5~2.0 h, and the secondary stirring temperature is 20~50℃.

13. The application of a medium-phase microemulsion according to any one of claims 1 to 7, or a medium-phase microemulsion obtained by the preparation method of the medium-phase microemulsion according to any one of claims 8 to 12, in the fields of oil and gas field development, deep water shut-off and profile control, or tertiary oil recovery.

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